With the advent of modern warfare, a battlefield has become an even more dangerous place. Unfortunately, this is true both for one's comrades-in-arms as well as for the enemy. Given the amount of firepower deployed in a battle zone, the constant movement of men and material, the rapidity with which tanks, personnel carriers, planes and helicopters move, and the inability to always know (regardless of the amount of effort employed) who is where, the chances of fratricidal harm being inflicted probably are higher than they have ever been. It thus has become imperative to limit, if not altogether eliminate, casualties resulting from “friendly” fire.
One way of discerning who is a friend and who is not is by use of an IFF (Identification Friend-or-Foe) system. Various IFF systems are well-known in the art. These typically are radio frequency (RF) transmission systems and, while principally associated with aircraft, the same technology is applicable to land based vehicles or ships. Certain RF systems, known as co-operative systems, involve transmitting an inquiry signal to an unknown object, e.g., an airplane, ship, tank, etc. If the object is a “friendly”, it has some type of transponder for responding to the inquiry with an appropriate reply. Upon receipt of an appropriate reply, the object is designated as friendly. If the object does not provide the required response, it is designated a foe and may be attacked.
Referring to FIG. 1, a battlefield 10 is illustrated in which both friendly and hostile forces are present. The friendly forces include, for example, a first tank 12, a second tank 14, a first personnel carrier 16, a second personnel carrier 18, and an attack plane 20. The hostile forces include a third tank 22, a fourth tank 24, and an attack helicopter 26.
The attack plane 20 carries an interrogator 30, e.g., a first portion of the IFF. The interrogator 30 emits a radio frequency (RF) signal, which generally is coded, on the battlefield. The signal is received and decoded by a transponder 32, e.g., a second portion of the IFF, which is located on (or in) friendly vehicles on the battlefield. In response to receiving the signal, each transponder transmits a signal back to the interrogator 30. If the interrogator 30 receives a proper reply from a vehicle's transponder 32, the vehicle is designated as a friendly. Conversely, if the interrogator 30 does not receive a reply or receives an improper reply from a vehicle's transponder, the vehicle is designated as a foe.
One drawback with co-operative systems is that it always is necessary for the object under inspection to have some mechanism for responding to an interrogation. A second drawback is that while co-operative IFF systems are the most positive types of identification systems and have been employed for a number of years in a variety of forms, they are not infallible. This is so for a number of reasons. For example, the response mechanism on the interrogated object may be inoperative or, because these type systems utilize codes, the code in the response mechanism may not be up-to-date. Consequently, the failure to respond to an interrogation signal cannot always be taken as an indication that the unknown object is hostile. As RF systems, they are vulnerable to jamming, they can be detected from many directions, thereby giving away the location of the weapon platform and, because of the power requirements of RF systems, they tend to be large.
To overcome some of these problems, other means of signal transmission have been employed, such as laser transmission systems. In laser systems, the laser beam replaces the RF as the medium for signal transmission, and the transponder is configured to receive the laser beam (as opposed to an RF signal). As the laser beam strikes the transponder, a portion of the laser beam is reflected back toward the source with a modulated response message. While this configuration is not susceptible to RF jamming, it is not infallible. Malfunctions and/or power loss in the transponder can prevent communications with the interrogator, thus allowing for potential errors in identification.
Another concern in the battlefield is the use of biological and/or chemical weapons. The threat of biological weapons as tools of modern warfare and urban terrorism is increasing. While the exact risks are unknown, the use of biological weapons by military adversaries and/or terrorists potentially could result in life-threatening illness and death on a large scale. Even a lone terrorist could cause a major disease outbreak in the population and, in the case of communicable disease, the outbreak could spread in successive waves of infection.
Unlike explosions or chemical releases, a bioterrorist attack could be surreptitious and thus difficult and time-consuming to detect. Symptoms might not occur among victims for days or weeks, and those initially presenting themselves to physicians and clinics might be geographically dispersed.
Development of early detection, counter measures, and remediation technology is a high priority in many military, government and private laboratories around the world. Biological warfare (BW) agents of critical concern are bacterial spores, such as Bacillus anthracis (anthrax), Clostridium tetani (tetanus), and Clostridium botulinum (botulism). Spores, produced by certain types of gram positive bacteria in response to starvation, are non-growing, heat-resistant, dehydrated, and resistant to extremes of temperature, pH, desiccation, radiation, and chemical agents. Due to their high stability, spores are difficult to stain using typical cell biology methods and, consequently, are challenging to detect and enumerate. This stability and difficulty with conventional detection methods, in turn, make them an attractive tool for use in biological weapons.
An effective bacterial spore detection method must be rapid, sensitive, selective, and cost-effective. In addition to these criteria, the technology must be easily incorporated into a handheld or field-portable device that has low power requirements, requires little maintenance, and provides reliable results.
Presently, vibrational spectroscopy is a useful technique for characterizing molecules and for determining their chemical structure. The vibrational spectrum of a molecule, based on the molecular structure of that molecule, is a series of sharp lines which constitutes a unique fingerprint of that specific molecular structure.
One particular spectroscopic technique, known as Raman spectroscopy, utilizes the Raman effect. The Raman effect is a phenomenon of inelastic light scattering. When light is scattered from a molecule most photons are elastically scattered, e.g., the scattered photons have the same frequency and, therefore, the same wavelength as the incident photons. A small fraction of light, however, is scattered at optical frequencies different from, and usually lower than, the frequency of the incident photons.
The Raman effect arises when a photon is incident on a molecule and interacts with the electric dipole of the molecule. Generally speaking, the Raman effect is very weak; approximately one photon out of one million will scatter from the sample at a wavelength slightly shifted from the original wavelengths.
Referring to FIG. 2, a significant increase in the intensity of Raman scattering 50 due to incident optical radiation 82 can be observed when molecules 54 are brought into close proximity to (but not necessarily in contact with) certain metal surfaces 56. This increase is known as surface enhanced Raman scattering (SERS). Enhancements by factors of 103 to 108 can be realized in the surface enhanced Raman scattering (SERS) intensity for adsorbates on or near special rough metal surfaces. This phenomenon has been verified for adsorbates at silver, copper, and gold metal surfaces under both solution and vacuum conditions.
It has been experienced, however, that because of the requirement for a metal surface for the SERS effect to be effective, most SERS media have limited usefulness in environments where the compounds do not adsorb easily onto the metal surface. Therefore, it has not been possible to utilize SERS media to monitor exposure to chemical compounds, such as many toxic organics, or biological species, such as bacteria or viruses, which do not adsorb easily onto a metal surface.
Accordingly, there is a need the art for an identification system that can identify biological and/or chemical compounds in a hostile environment as well as a civilian environment. Furthermore, there is a need in the art for an identification system that reliably can classify objects as friend-or-foe without being susceptible to presently known jamming techniques.